The formation and action of cyclic nucleotides in several systems will be examined. Studies will emphasize the regulation of cyclic GMP synthesis and functions. Guanylate cyclase will be purified and characterized and its regulation examined. Antibodies developed to guanylate cyclase will be used to examine antigenic similarities of soluble and particulate forms of the enzyme, purification, enzyme turnover, and immunohistochemical localization. Cyclic nucleotide metabolism in patients with various clinical disorders will also be examined.